Superposed sheet detector

ABSTRACT

Improved superposed sheet detecting apparatus is provided in accordance with the teachings of the present invention. Transducer means disposed in operable location to sheet feeding mechanism is adapted to produce signals proportional to the thickness of sheets of material fed past the operable location. A multibit binary signal representative of the thickness of an initially fed sheet of material is gated into storage means whereat said multibit binary signal is stored. Multibit binary signals representative of the thickness of subsequently fed sheets of material are compared to the stored multibit binary signal by comparison means. When the thickness of a subsequently fed sheet of material exceeds the thickness of an initially fed sheet of material the comparison means produces an error signal, which error signal is detected by activatable detecting means. Detection of the error signal may result in the deflection of the subsequently fed sheet of material from the sheet feeding mechanism.

llnited States Patent 1 1 1111 3,778,051 Allen et al. Dec. 11, 1973SUPERPOSED SHEET DETECTOR [76] Inventors: James H. Allen, 17 MaryvaleDr., [57] ABSTRACT Webster; Dememos Polyzoes 12 Improved superposedsheet detecting apparatus is progugermllk Plttsford both of vided inaccordance with the teachings of the present invention. Transducer meansdisposed in operable lo- [22] Filed: Oct. 21, 1971 cation to sheetfeeding mechanism is adapted to produce signals proportional to thethickness of sheets of [211 App]' 19l459 material fed past the operablelocation. A multibit binary signal representative of the thickness of anini- [52] US. Cl. 271/57, 235/92 SB tially fed sheet of material isgated into storage means [51] Int. Cl. B65h 7/12, G06f 7/38 whereat saidmultibit binary signal is stored. Multibit [58] Field of Search 271/57;209/74 R, binary signals representative of the thickness of subse-209/82; 83/371; 235/92 SB quently fed sheets of material are compared tothe stored multibit binary signal by comparison means.

[56] References Cited When the thickness of a subsequently fed sheet ofma- UNITED STATES PATENTS terial exceeds the thickness of an initiallyfed sheet of 3 182 301 5/1965 Kolb 271 57 x material the compfirison.means produces 3" 3:460:67?) 3/1969 Same. t 209/74 R x nal, which errorsignal 1s detected by activatable de- 3,l76,839 4/1965 Whitecar 209/74 Rtwins means- Detection of the error Signal y result 3,616,901 11 1971Groves 209 74 M in th d fl ti n of the subsequently fed sheet ofmaterial from the sheet feeding mechanism.

Primary ExaminerEdward A. Sroka Attorney-James J. Ralabate et al. 17Claims 2 D wing Figures 2/6 2/5 Activate o'- 2/7 AND /2/2 lncrernenlo2/0 Gate c A? 206 1 Sample 0--- Gale 1 AND 209 y l 1 Analog AND I Com622: 1 store purutor 1 1 AND 1 209 I AND 2/3 J Reset c Pmmwml Haws sum11! 2 INVENTORS James H. Allen Demetrios Polyzoes 7724M &

ATTORNEYS SUPERPOSED SHEET DETECTOR This invention relates to improvedsuperposed sheet detecting apparatus, and more particularly, to improvedapparatus for detecting the transporting of superposed sheets ofmaterial admitting of selectively variable thicknesses.

The successful operation of devices such as printing presses, copyreproducing machines and the like that operate upon sheets of materialserially fed thereto is dependent upon the feeding of single sheets ofmaterial. In addition, it is preferable that these devices exhibit thecapability of operating upon sheets of material admitting of variousweights and thicknesses. Most sheet feeding mechanisms developed by theprior art, although designed to transport single sheets of material,occasionally convey superposed sheets.

Thus it has been necessary to employ a superposed sheet detector inconjunction with sheet transport means to prevent superposed sheets frombeing operated upon by the aforementioned devices. Conventionaldetecting means heretofore utilized by the prior art employ mechanicalmembers that are preset to specific tolerances. Single sheets having athickness that correspond to such tolerances are passed through thedetecting means while superposed sheets are diverted therefrom. Thesedetectors however, limit the sheets that may be employed therewith tospecific thicknesses. If material admitting of a thickness that does notcorrespond to the preset specific tolerances is to be utilized, askilled technician must effect the necessary mechanical adjustments.Hence, these detectors do not permit rapid interchangeability betweenvarious types of material. Moreover, it has been found that these priorart superposed sheet detectors are not responsive to superposed sheetsof relatively thin material whereas single sheets of relatively thickmaterial erroneously activate the detector.

In U.S. Pat. application Ser. No. 180,973 entitled Superposed SheetDetection, filed on Sept. I6, 1971 by James H. Allen and assigned toXerox Corporation, the assignee of the present invention, there aredescribed various techniques that successfully overcome the foregoingdisadvantages. The present invention is drawn to improve superposedsheet detecting apparatus for detecting superposed sheets of materialadmitting of selectively variable thicknesses.

Therefore, it is an object of the present invention to provide improvedsuperposed sheet detecting apparatus.

It is a further object of this invention to provide improved superposedsheet detecting apparatus capable of detecting a multiple of sheetsadmitting of selectively variable thicknesses.

It is a further object of the present invention to provide improvedsuperposed sheet detecting apparatus adapted to prevent the feeding ofsingle sheets of material having an undesired thickness.

Still another object of the present invention is to provide electricalapparatus for detecting superposed sheets of material, which apparatusdoes not require mechanical adjustment.

Yet another object of this invention is to provide improved apparatusfor detecting superposed sheets of various types of material.

It is an additional object of the present invention to provide improvedsuperposed sheet detecting apparatus employing digital circuitry.

Various other objects and advantages of the invention will become clearfrom the following detailed description of an exemplary embodimentthereof, and the novel features will be particularly pointed out inconnection with the appended claims.

In accordance with this invention, improved superposed sheet detectingapparatus for detecting the superposition of transported sheets ofmaterial admitting of selectively variable thicknesses is providedwherein multibit binary signals representative of the thickness oftransported sheets of material are generated; the multibit binary signalrepresentative of the thickness of an initially transported sheet ofmaterial is stored in storage means; comparison means compares thecontent of the storage means with each generated multibit binary signaland produces an error signal when a multibit binary signal exceeds thecontents of the storage means; and activatable detecting means respondsto an activating signal supplied thereto to detect a produced errorsignal.

The invention will be more clearly understood by reference to thefollowing detailed description of an exemplary embodiment thereof inconjunction with the accompanying drawings in which:

FIG. 1 schematically illustrates a portion of a reproducing devicewherein the improved superposed sheet detecting means of the presentinvention may be employed; and

FIG. 2 is a diagram in partial schematic and partial block form of adigital circuit in accordance with the present invention.

Referring now to the drawings, and in particular to FIG. 1, there isshown automatic reproducing apparatus such as an electrophotographicreproducing machine which comprises a photoreceptive plate 20 includinga photoconductive layer or a light receiving surface on a conductivebacking and formed in the' shape of a drum, adapted to rotate in thedirection indicated by the arrow to cause the drum'surface tosequentially pass a plurality of processing stations. It is noted hereinthat FIG. 1 corresponds to an identical figure in aforementionedapplication Ser. No. 180,973. Accordingly, reference may be had to thatapplication for a more detailed description of the illustratedapparatus. Briefly, however, the several processing stations in the pathof movement of the drum surface comprise a charging station 21 fordepositing a uniform electrostatic charge on the photoreceptive drum 20.An exposure station including an object mirror 23, image mirror 25 andlight shield 26 is provided to dissipate the electrostatic charge inaccordance with a projected light image of a document 22. A developingstation 30, provided with conventional developing material such as tonerparticles, is provided to form a powder image in the configuration ofthe electrostatic latent image formed on the surface of thephotoreceptive drum 20. The powder image is transferred from the surfaceof drum 20 to the surface of a sheet of material in intimate contacttherewith, said sheet of material being transported to a transferstation by sheet feeding mechanism soon to be described. The transferstation includes a corona transfer device 21 adapted to produce anelectrostatic field which is capable of attracting the toner particlesfrom the surface of the drum 20 to the surface of the sheet of material.Stripping apparatus 52 is adapted to remove a sheet of material from thesurface of the drum 20 and to direct the sheet of material onto endlessmovable belt means 53, whereby the sheet of material is carried to afixing station (not shown). A cleaning station including a coronapre-cleaning means 60, rotating brush 6] and discharge lamp 63 isprovided to remove residual powder from the surface of drum 20 and toflood the drum with light to cause dissipation of any residual electriccharge remaining on the surface thereof.

The sheet feeding mechanism includes a sheet feed device 40 adapted tofeed the top sheet 401 of a stack of sheets to roller means 42. Endlessmovable belt means 41 is deployed about roller means 42 and serves totransport the sheet fed to roller means 42 to a sheet registrationdevice 45. The sheet transported by endless belt means 41 is adapted toadhere thereto by means of vacuum shoe 44. The sheet transport deviceincludes sensing means 47 disposed at a fixed location therein andadapted to sense the leading edge of a sheet transported by endless beltmeans 41. Sensing means 47 may comprise a conventional switch includinga depending lever interposed in the path of the transported sheets.Contact between the leading edge of a sheet and the depending lever iseffective to close the switch. Alternatively, sensing means 47 mayinclude a photoelectric device wherein a light beam may be interruptedby the leading edge of a transported sheet, resulting in the closing ofa switch or generation of a pulse signal. The sheet transport devicefurther includes reject fingers 46 which are adapted to protrude intothe path of a conveyed sheet upon being actuated. The movement of rejectfingers 46 into the path of a conveyed sheet is effective to deflect thesheet into an abort or reject tray 400 located beneath the sheettransport device.

Transducer means 101 is disposed at a predetermined location in thesheet feeding mechanism and is adapted to produce signals proportionalto the thickness of the sheets of material transported past thepredetermined location. Transducer means 101 may comprise a rotatablemember in spaced registration from roller means 42 whereby the rotatablemember is angularly displaced by an amount dependent upon the thicknessof a sheet of material interposed between the rotatable member and theroller means 42. The rotatable member may be operably coupled tovariable impedance means such that the impedance of the variableimpedance means is varied in accordance with the angular displacement ofthe rotatable member. The variable impedance means may, in turn, becoupled to a detecting network capable of producing an analog signalhaving a magnitude that varies in accordance with the impedance of thevariable impedance means. The foregoing transducer means comprised ofthe rotatable member, variable impedance means and detecting network isdescribed in more detail in the aforementioned US. Pat. application Ser.No. 180,973.

Transducer means 101 may comprise other conventional means adapted toproduce a signal proportional to the thickness ofa sheet of material.Accordingly, the transducer means 101 may comprise a proximity detectorwherein a change in the separation between transducer means 101 and areference such as roller means 42 caused by the feeding of a sheet ofmaterial therebetween effects a corresponding change in the amplitude ofan analog signal. Conventional proximity detectors employing capacitiveor inductive coupling are well known in the prior art and need not befurther described herein. A further alternative of transducer means 101may comprise a conventional weight detector wherein the weight of asheet of material placed thereon depresses the transducer means and ananalog signal proportional thereto is produced.

The signal produced by transducer means 101 is applied to the digitalcircuitry illustrated in FIG. 2 which comprises binary signal generatingmeans 207, selectively activatable gating means 209, storage means 211,comparison means 214 and activatable detecting means 215. Binary signalgenerating means 207 is adapted to generate a multibit binary signalcomprised of any convenient number of bits in response to the analogsignal produced by transducer means 101. Accordingly, the binary signalgenerating means may comprise a conventional analog to digital converterwell known to those of ordinary skill in the art and capable ofproducing a multibit binary signal representative of the analog signalapplied thereto when a sample pulse is supplied to terminal 208. Inaddition, the multibit binary signal generated thereby may be a serialbinary signal comprised of a train of binary ones and zeros or aparallel binary signal wherein the binary ones and zeros are generatedsimultaneously. It will soon become apparent that it is preferable toemploy an analog to digital converter wherein the multibit binary signalgenerated thereby is comprised of a plurality of parallel binary onesand zeros. Binary signal generating means 207 is coupled to inputterminals 201, 202 via filter means 203. The filter means 203 functionsas a low pass filter for removing rapid variations in the analog signalapplied to terminals 201, 202 by transducer means 101. It will beappreciated by those of ordinary skill in the art that such signalvariations correspond to small surface irregularities in the sheet ofmaterial transported past the transducer means. In addition, filtermeans 203 produces a signal corresponding to the thickest portion of thetransported sheet of material. Hence, filter means 203 may include aconventional amplitude modulation detector comprised of diode 204 havingan anode coupled to input terminal 201 and a cathode coupled to parallelconnected capacitance means 205 and resistance means 206. The timeconstant of the parallel connected capacitance means 205 and resistancemeans 206 may be chosen such that capacitance means 205 is capable ofcharging to the maximum amplitude applied to input terminal 201. In theconfiguration illustrated in FIG. 2 it is assumed that the analog signalproduced by transducer means 101 and applied to input terminal means201, 202 is a positive signal. If, however, the analog signal is anegative signal, diode 204 may be oppositely poled such that the cathodethereof is coupled to input terminal 201 and the anode thereof iscoupled to the parallel connected capacitance means 205 and resistancemeans 206.

Binary signal generating means 207 is coupled to selectively activatablegating means 209 which performs a switching function adapted to applythe multibit binary signal supplied to the input terminals thereof tothe output terminals thereof in response to a gating signal applied toterminal 210 at selected intervals of time. Selectively activatablegating means 209 is comprised of a plurality of AND gates 209a 209ncorresponding in number to the number of parallel binary bits includedin each multibit binary signal. Each of the AND gates 209a 209n includesa first input terminal coupled to the binary signal generating means 207for receiving an associated one of the bits included in the multibitbinary signal and a second input terminal coupled to terminal 210. Asillustrated herein, the second input terminals of AND gates 209a 209nare connected in common relationship. It is appreciated that if themultibit binary signal is comprised of a train of serially generatedbits, the selectively activatable gating means 209 may comprise a singleAND gate.

Storage means 211 includes a plurality of input terminals coupled toselectively activatable gating means 209, and is adapted to store themultibit binary signal generated by binary signal generating means 207and gated thereto by selectively activatable gating means 209. Thestorage means 211 may comprise a conventional buffer register having anumber of stages corresponding to the number of bits included in themultibit binary signal. If the multibit binary signal is comprised of aplurality of parallel bits, the storage means 211 simultaneously storeseach of the bits in an associated register stage. Alternatively, if themultibit binary signal is comprised of a train of serially generatedbits, the storage means 211 may comprise a conventional shift registerthrough which the train of bits is serially shifted. For a purpose to bedescribed, it is preferable that storage means 211 comprises a settablecounting means capable of being set to a binary count corresponding tothe multibit binary signal gated thereto, and wherein the binary countmay be incremented in response to counting pulses supplied to terminal212. Thus, the storage means 211 may comprise a parallel/- serial shiftregister wherein the output of selectively activatable gating means 209is stored therein in parallel as a binary number, and the binary numberis serially increased in accordance with the incrementing pulses appliedto terminal 212.

Storage means 211 additionally includes a reset input terminal coupledto input terminal 213. A reset pulse applied to input terminal 213 iseffective to clear the contents of storage means 211, thereby resettingthe storage means to a quiescent condition.

Comparison means 214 includes a first plurality of input terminalscoupled to the storage means 211 and a second plurality of inputterminals coupled to the binary signal generating means 207. Comparisonmeans 214 is adapted to compare the contents of the storage means211with each multibit binary signal generated by the binary signalgenerating means 207 and to produce an error signal when the generatedmultibit binary signal exceeds the contents of the storage means.Accordingly, comparison means 214 may comprise a logic subtractorcircuit formed of a plurality of AND gates and OR gates such asdescribed at page 158 of Design of Digital Computers by H. W. Gschwind,1967, capable of performing the aforenoted function. Those of ordinaryskill in the art are clearly competent in constructing an alternativecircuit such as an analog comparator including digital-to-analogconverters coupled to storage means 211 and binary signal generatingmeans 207, respectively. Since the precise structure of the comparisonmeans 214 forms no part of the present invention per se, furtherdescription thereof is not necessary for a complete understanding of thepresent in vention. The output terminal of comparison means 214 to whichan error signal is applied is coupled to activatable detecting means215. The activatable detecting means 215 is adapted to detect the errorsignal supplied thereto and to energize further means coupled to lead217 in response to the detected error signal. The activatable detectingmeans 215 may comprise a conven' tional AND gate including a first inputterminal coupled to terminal 216 to which an activating signal isapplied, such that error signals supplied to the second input terminalof the AND gate are detected at selected intervals of time. Lead 217 maybe connected to a conventional solenoid means (not shown) which solenoidmeans is operably coupled to reject fingers 46 of FIG. 1. Thus, it maybe appreciated that the detection of an error signal by activatabledetecting means 215 results in the projection of reject fingers 46 intothe path of travel of a sheet of material transported by the sheetfeeding mechanism.

The operation of the digital circuit illustrated in H0. 2 will now bedescribed in conjunction with FIG. 1. When operation of the apparatusemploying the sheets of material is initiated, the top sheet 401 is fedto the sheet transport device by sheet feeding means 40. Transducermeans 101 senses the presence of the transported sheet of material andproduces an analog signal having an amplitude proportional to thethickness of the sensed sheet of material. The analog signal is appliedto terminals 201, 202 and filter means 203 removes the rapid variationstherein such that binary signal generating means 207 is supplied with asignal representing the actual thickness of a transported sheet. Asample pulse is applied to terminal 208 once during each transportingcycle of the sheet feeding means 40. Accordingly, a multibit binarysignal is generated by the binary signal generating means 207 at eachsample pulse time, which multibit binary signal is representative of thethickness of each transported sheet of material. A gating signal isapplied to terminal 210 in time delayed relationship with respect to theapplication of the sample pulse to terminal 208 whereby selectivelyactivatable gating means 209 is activated to gate the multibit binarysignal generated by binary signal generating means 207 into storagemeans 211. It should be noted that the gating signal is applied toterminal 210 only when an initially transported sheet of material is fedby the sheet feeding mechanism. Thus, only the multibit binary signalrepresentative of the thickness of an initially transported sheet ofmaterial is stored in storage means 211.

The multibit binary signal is stored as a corresponding binary count bythe storage means 211. The contents of the storage means 211 arecompared in comparison means 214 to the multibit binary signal generatedby the binary signal generating means 207. Since only the initiallygenerated multibit binary signal is stored in storage means 211 it isreadily seen that the initial signal is compared to each subsequentlygenerated multibit binary signal. Hence, comparison means 214 effects acomparison between the thickness of an initially transported sheet ofmaterial and the thickness of each subsequently transported sheet ofmaterial. When the thickness of a subsequently transported sheet ofmaterial exceeds that of the initially transported sheet of material,comparison means 214 applies an error signal to activatable detectingmeans 215. It is understood that when an initial sheet of material istransported, the multibit binary signal applied to comparison means 214by binary signal generating means 207 is equal to the multibit binarysignal stored in storage means 211 and applied to comparison means 214.Accordingly, it is expected that comparison means 214 will not producean error signal at this time. However, it has been found that thedigital circuitry illustrated in FIG. 2 exhibits inherent time delaycharacteristics such that the multibit binary signal generated by binarysignal generating means 207 might be applied to comparison means 214before storage means 211 is able to complete its storage operation ofthat multibit binary signal. Hence, it is possible that comparison means214 might produce an error signal during the feeding of an initial sheetof material. Activatable detecting means 215 however, cannot respond tothe error signal supplied thereto unless an activating signal is appliedto terminal 216. Accordingly, it is contemplated that terminal 216 willreceive an activating signal during the transport of each sheet ofmaterial except the initially transported sheet of material.Consequently, the production of an error signal by comparison means 214in response to the feeding of an initially transported sheet of materialpast the transducer means 101 will have no effect on the operation ofthe apparatus illustrated in FIGS. 1 and 2.

Let it now be assumed that superposed sheets of material are transportedby the sheet feeding mechanism. Transducer means 101 will produce ananalog signal which analog signal is sampled by binary signal generatingmeans 207 when a sample pulse is applied to terminal 208, therebygenerating a multibit binary signal representative of the totalthickness of the superposed sheets. Selectively activatable gating means209 prevents this multibit binary signal from being applied to storagemeans 211 because a gating pulse is applied to terminal 210 only duringthe transport of an initial sheet of material. The multibit binarysignal is however supplied to comparison means 214 whereat it iscompared to the stored multibit binary signal. Thus, the total thicknessof the superposed sheets of material is compared to the thickness of asingle initially transported sheet of material. It is appreciatedtherefore, that comparison means 214 applies an error signal toactivatable detecting means 215. Upon receiving an activating signalsupplied to terminal 216, the activatable detecting means 215 applies apulse signal to lead 217. The pulse signal is effective to energizereject fingers 46 of FIG. 1 to deflect the superposed sheets of materialaway from the sheet feeding mechanism and into reject tray 400.

It is observed that the thickness of single sheets of material may varythroughout a permissible range of thicknesses. Consequently, if aninitially transported single sheet of material admits of a relativelythin thickness and a subsequently transported single sheet of materialadmits of a relatively thick thickness then the multibit binary signalapplied to comparison means 214 by binary signal generating means 207will exceed the multibit binary signal supplied to comparison means 214by storage means 211 such that an error signal is detected byactivatable detecting means 215, thereby projecting reject fingers 46into the path of the subsequently transported single sheet of material.It is a feature of the present invention to permit single sheets ofmaterial exhibiting a range of thicknesses to be successfullytransported without the erroneous rejecting thereof. Thus, asubsequently transported sheet of material is assumed to be comprised ofsuperposed sheets ifthe sensed thickness thereof exceeds the thicknessof an initially transported sheet by a predetermined amount. In otherwords, the multibit binary signal generated by binary signal generatingmeans 207 must exceed the multibit binary signal stored in storage means211 by a threshold amount before the activatable detecting means 215energizes reject fingers 46. Although various techniques may be employedto provide for the aforementioned threshold, such as by providing binarysignal generating means 207 with a high degree of quantization whilediscarding the least significant bits of the highly quantized multibitbinary signal generated thereby, it is preferred to increase the valueof the multibit binary signal stored in storage means 211 by apredetermined amount. Thus, the binary count that is set in storagemeans 211 by the multibit binary signal supplied thereto by selectivelyactivatable gating means 209 is incremented to a higher binary count bysupplying incrementing pulses to terminal 212. It is appreciated thatthe number of incrementing pulses applied to terminal 212 may bedetermined by the permissible range of thicknesses of single sheets ofmaterial. Thus, if a relatively wide range of thicknesses ispermissible, a correspondingly large number of increment pulses isapplied to terminal 212. Conversely, if a relatively narrow range ofthicknesses is permissible, a correspondingly small number of incrementpulses is applied to terminal 212. Hence, the increment pulses determinethe threshold thickness which must not be exceeded by a single sheet ofmaterial. As an illustrative example, let it be assumed that thethickness of an initially transported sheet of material is representedby the count 1001 stored in storage means 21]. Those skilled in the artof binary notation will understand that this corresponds to a count of9. Let it further be assumed that a single sheet of material admittingof a thickness corresponding to a count of 12, Le, l 100, is a maximumpermissible thickness. If now the thickness of a subsequentlytransported sheet of material is represented by the binary count 1010(corresponding to the count of 10) an error signal would be produced bycomparison means 214. Therefore, after the binary count 1001corresponding to the multibit binary signal representative of thethickness of the initially transported sheet of material is stored instorage means 211, three incrementing pulses are applied to terminal 212such that the count now stored by storage means 211 is incremented to1100. Consequently, an error signal will not be produced by comparisonmeans 214 in response to the subsequently transported sheet of materialunless the subsequently transported sheet of material admits of athickness represented by the multibit binary signal 1 101 (correspondingto a count of 13), which thickness is assumed to be indicative ofsuperposed sheets.

After a perdetermined number of sheets have been transported past thetransducer means 101, a reset pulse may be applied to terminal 213 toclear the multibit binary signal stored in storage means 211. This maybe accomplished by connecting a conventional counting means to sensingmeans 47 such that the number of sheets sensed by sensing means 47 iscounted by the counting means. When a predetermined count is obtainedthe reset pulse may be applied to terminal 213. Alternatively, a resetpulse might be applied to terminal 213 when the apparatus illustrated inFIG. 1 completes an operating cycle. The operating cycle might beindependent of the total number of sheets transported by the sheetfeeding mechanism 40. Thus, the contents of storage means 211 might bediscarded after a predetermined number of sheets have been transportedor after the completion of an operating cycle, notwithstanding thenumber of sheets of material that have been deflected by reject finger46. Another embodiment contemplates the connection of terminal 213 tolead 217 such that detection of an error signal by activatable detectingmeans 215 results in the clearing of the multibit binary signal storedin storage means 211. It is appreciated that when a reset pulse isapplied to terminal 213 to clear the contents of storage means 211, thedigital circuit illustrated in FIG. 2 is returned to its quiescentcondition. The next sheet of material transported by the sheet feedingmechanism is assumed to be an initially transported sheet and theforegoing operation of the digital circuit illustrated in FIG. 2 isrepeated. Hence, the interconnection of terminal 213 and lead 217 iseffective to establish a detecting cycle for the illustrated circuitwhich detecting cycle is initiated by a first transported sheet ofmaterial and terminated when activatable detecting means 215 detects anerror signal produced by comparison means 214. Thedetecting cycle,however, does not admit of a predetermined duration, but is dependentupon the detection of superposed sheets. i

It is now understood that the operation of the present invention isdependent upon the thickness of an initially transported single sheet ofmaterial. Determinations as to the superposition of subsequentlytransported sheets are made on the basis of the thickness of an initialsheet. Thus, a stack of thin sheets of material may be interchanged witha stack of thick sheets of material without necessitating mechanicaladjustments of the present invention because the initial sheet of thinmaterial provides a reference for the subsequently transported thinsheets and the initial sheet of thick material provides a reference forthe subsequently transported thick sheets. The present inventionadditionally provides for the possibility that an initially transportedsheet is, in fact, comprised of superposed sheets. If the referencemultibit binary signal stored in storage means 211 is representative ofthe thickness of superposed sheets, the multibit'binary signalsgenerated by binary signal generating means 207 and representative ofthe thickness of subsequently transported sheets might not 1 exceed thereference multibit binary signal and an error signal might not beproduced by comparison means 214. It will be observed however, thatstripping apparatus 52 of FIG. 1 will remove only the overlying one ofthe superposed sheets. Consequently, the underlying sheet of materialadhering to the surface of the photoreceptive drum 20 will be detectedby photodetecting means 64 as described in detail in aforementioned U.S.Pat. application Ser. No. 180,973. The thus detected adhering sheetmight result in the application of a reset pulse to terminal 213 wherebythe contents of storage means 211 are cleared therefrom. The digitalcircuit illustrated in FIG. 2 is thus returned to its quiescentcondition and is prepared to execute a subsequent detecting cycle. Ofcourse, the foregoing may be obviated by insuring that the initial sheetof material is in fact a single sheet. This may be achieved by providinga sample sheet of material representing the desired thickness ofsubsequently transported single sheets, which sample sheet is fed to thesheet transport device by an operator.

The sample signal applied to terminal 208, gating signal applied toterminal 210, increment pulses applied to terminal 212 and activatingsignal applied to terminal 216 may be applied thereto in predeterminedtimed relation. These signals may be generated by preset programmingmeans such as that described in U.S. Pat. No. 3,301,126 which issued toR. F. Osborn, et al. on Jan. 31, 1967 and assigned to Xerox Corporation.

It should be apparent to those of ordinary skill in the art that theinstant invention admits of a plurality of alterations and modificationswhich in no way change the basic teachings thereof. For example, shouldthe transducer means 101 be insensitive to minor surface irregularitiesin the sheets of material transported by the sheet feeding mechanism,such that the analog signal produced thereby exhibits a relativelyconstant amplitude, then filter means 203 may be omitted. In addition,comparison means 215 may be effective to produce an error signal whenthe multibit binary signal stored in storage means 211 exceeds themultibit binary signal produced by binary signal generating means 207 bya predetermined amount. Thus, if a subsequently transported sheet ofmaterial admits of a thickness that is undesirably thin, i.e., thesubsequently transported sheet is too thin with respect to an initial orreference sheet, such sheet will be deflected from the tranportingdevice illustrated in FIG. 1. Moreover, while the invention has beenparticularly shown and described with reference to printing presses andto electrophotographic reproducting machines, it will be obvious thatthis invention may be utilized with any device wherein the thickness ofmaterial or detection of superposed sheets is desirable. Consequently,it is apparent that the foregoing and various other changes andmodifications in form and details may be made without departing from thespirit and scope of the invention. It is therefore intended that theappended claims be interpreted as including all such changes andmodifications.

What is claimed is:

1. Improved superposed sheet detecting apparatus for detecting thesuperposition of transported sheets of material, said sheets of materialadmitting of selectively variable thicknesses, comprising:

binary signal generating means for generating multibit binary signalsrepresentative of the thickness of transported sheets of material,

storage means for storing the multibit binary signal representative ofthe thickness of an initially transported sheet of material;

selectively activatable gating means interconnected between said binarysignal generating means and said storage means for selectively gating amultibit binary signal generated by said binary signal generating meansinto said storage means;

comparison means having a first plurality of input terminals coupled tosaid storage means and a second plurality of input terminals coupled tosaid binary signal generating means for comparing the contents of saidstorage means with each multibit binary signal generated by said binarysignal generating means and for producing an error signal when agenerated multibit binary signal exceeds said contents of said storagemeans; and

activatable detecting means coupled to said comparison means andresponsive to an activating signal supplied thereto to detect said errorsignal.

2. The improvement of claim 1 wherein said storage means comprises:

settable counting means having a plurality of input terminals coupled tosaid selectively activatable gating means, said settable counting meansbeing set to a binary count corresponding to said multibit binary signalrepresentative of the thickness of an initially transported sheet ofmaterial; and

increment means coupled to said settable counting means for incrementingthe set binary count thereof such that predetermined variations in thethickness of subsequently transported sheets of material do not produceerror signals.

3. The improvement of claim 1 wherein said binary signal generatingmeans comprises:

transducer means for producing an analog signal proportional to thethickness of transported sheets of material;

filter means coupled to said transducer means for removing rapidamplitude variations exhibited by said analog signal; and

analog to digital converting means coupled to said filter means forgenerating a multibit binary signal proportional to said analog signal.

4. The improvement of claim 1 wherein said selectively activatablegating means comprises a plurality of AND gates corresponding in numberto the number of bits included in each multibit binary signal; said ANDgates including first input terminals for receiving associated ones ofsaid bits included in a multibit binary signal and second inputterminals connected in common relationship for receiving a gating signalsupplied thereto at selected intervals of time.

5. The improvement of claim 1 wherein said activatable detecting meanscomprises an AND gate having a first input terminal for receiving saiderror signal and a second input terminal for receiving an activatingsignal supplied thereto at selected intervals of time.

6. In combination with a sheet feeding mechanism, improved superposedsheet detecting apparatus for detecting the superposition of sheets ofmaterial fed by said sheet feeding mechanism, comprising:

transducer means disposed at a predetermined location in said sheetfeeding mechanism for producing signals proportional to the thickness ofsheets of material fed past said predetermined location; binary signalgenerating means coupled to said transducer means for generatingmultibit binary signals representative of said produced signals; storagemeans for storing the multibit binary signal representative of aninitially produced signal;

selectively activatable gating means interconnected between said binarysignal generating means and said storage means for selectively gating amultibit binary signal generated by said binary signal generating meansinto said storage means;

comparison means having a first plurality of input terminals coupled tosaid storage means and a second plurality of input terminals coupled tosaid binary signal generating means for comparing the contents of saidstorage means with each multibit binary signal generated by said binarysignal generating means and for producing an error signal when agenerated multibit binary signal differs from said signal of saidstorage means;

activatable detecting means coupled to said comparison means andresponsive to an activating signal supplied thereto to detect said errorsignal;

deflecting means coupled to said activatable detecting means and adaptedto be interposed in the path of said sheets of material fed by saidsheet feeding mechanism in response to a detected error signal fordeflecting the sheets of material away from said sheet feedingmechanism; and

means for discarding the contents of said storage means. 7. Thecombination of claim 6 wherein said storage means comprises:

settable counting means having a plurality of input terminals coupled tosaid selectively activatable gating means, said settable counting meansbeing set to a binary count corresponding to said multibit binary signalrepresentative of the thickness of an initially transported sheet ofmaterial; and

increment means coupled to said settable counting means for incrementingthe set binary count thereof such that predetermined variations in thethickness of subsequently transported sheets of material do not produceerror signals.

8. The combination of claim 7 wherein said binary signal generatingmeans comprises:

filter means coupled to said transducer means for removing rapidamplitude variations exhibited by each of said signals produced by saidtransducer means; and

sample means coupled to said filter means for sampling at first selectedintervals of time the signal produced by said filter means and forgenerating a parallel multibit binary signal proportional to saidamplitude.

9. The combination of claim 8 wherein said selectively activatablegating means comprises a plurality of AND gates corresponding in numberto the number of bits included in each multibit binary signal; said ANDgates including first input terminals for receiving associated ones ofsaid bits included in said parallel multibit binary signal and secondinput terminals connected in common relationship for receiving a gatingsignal supplied thereto at second selected intervals of time.

10. The combination of claim 9 wherein said activatable detecting meanscomprises an AND gate having a first input terminal for receiving saiderror signal and a second input terminal for receiving an activatingsignal supplied thereto at third selected intervals of time; said ANDgate being deactivated when an initial sheet of material is fed pastsaid predetermined location.

11. The combination of claim 10 wherein said means for discardingcomprises reset means for receiving a reset pulse when a predeterminednumber of sheets have been fed past said predetermined location, saidreset pulse being effective to clear said multibit binary signal fromsaid storage means.

12. The combination of claim 10 wherein said means for discardingcomprises reset means for receiving a reset pulse when said error signalis detected, said reset pulse being effective to clear said multibitbinary signal from said storage means.

13. In combination with a sheet feeding mechanism, improved superposedsheet detecting apparatus for detecting the superposition of sheets ofmaterial fed by said sheet feeding mechanism, comprising:

transducer means disposed at a predetermined location in said sheetfeeding mechanism for producing signals proportional to the thickness ofsheets of material fed past said predetermined location;

binary signal generating means coupled to said transducer means forgenerating multibit binary signals representative of said producedsignals;

storage means for storing the multibit binary signal representative ofan initially produced signal;

selectively activatable gating means interconnected between said binarysignal generating means and said storage means for selectively gating amultibit binary signal generated by said binary signal generating meansinto said storage means;

comparison means having a first plurality of input terminals coupled tosaid storage means and a second plurality of input terminals coupled tosaid binary signal generating means for comparing the contents of saidstorage means with each multibit binary signal generated by said binarysignal generating means and for producing an error signal when agenerated multibit binary signal differs from said signal of s stpra m vM- i Y,

activatable detecting means coupled to said comparison means andresponsive to an activating signal supplied thereto to detect said errorsignal; and

means coupled to said activatable detecting means and responsive to saiddetected error signal for preventing the further feeding of said sheetsof material by said sheet feeding mechanism.

14. The combination of claim 13 further including reset means forreceiving a reset pulse when said error signal is detected, said resetpulse being effective to clear said multibit binary signal from saidstorage means.

15. The combination of claim 13 wherein said storage means comprises:

settable counting means having a plurality of input terminals coupled tosaid selectively activatable gating means, said settable counting meansbeing set to a binary count corresponding to said multibit binary signalrepresentative of the thickness of an initially transported sheet ofmaterial; and increment means coupled to said settable counting meansfor incrementing the set binary count thereof such that predeterminedvariations in the thickness of subsequently transported sheets ofmaterial do not produce error signals. 16. The combination of claim 13wherein said binary signal generating means comprises:

filter means coupled to said transducer means for removing rapidamplitude variations exhibited by each of said signals produced by saidtransducer means; and sample means coupled to said filter means forsampling at first selected intervals of time the signal produced by saidfilter means and for generating a parallel multibit binary signalproportional to said amplitude. 17. The combination of claim 13 furtherincluding means for discarding the contents of said storage means when apredetermined number of sheets have been fed past said predeterminedlocation.

1. Improved superposed sheet detecting apparatus for detecting thesuperposition of transported sheets of material, said sheets of materialadmitting of selectively variable thicknesses, comprising: binary signalgenerating means for generating multibit binary signals representativeof the thickness of transported sheets of material; storage means forstoring the multibit binary signal representative of the thickness of aninitially transported sheet of material; selectively activatable gatingmeans interconnected between said binary signal generating means andsaid storage means for selectively gating a multibit binary signalgEnerated by said binary signal generating means into said storagemeans; comparison means having a first plurality of input terminalscoupled to said storage means and a second plurality of input terminalscoupled to said binary signal generating means for comparing thecontents of said storage means with each multibit binary signalgenerated by said binary signal generating means and for producing anerror signal when a generated multibit binary signal exceeds saidcontents of said storage means; and activatable detecting means coupledto said comparison means and responsive to an activating signal suppliedthereto to detect said error signal.
 2. The improvement of claim 1wherein said storage means comprises: settable counting means having aplurality of input terminals coupled to said selectively activatablegating means, said settable counting means being set to a binary countcorresponding to said multibit binary signal representative of thethickness of an initially transported sheet of material; and incrementmeans coupled to said settable counting means for incrementing the setbinary count thereof such that predetermined variations in the thicknessof subsequently transported sheets of material do not produce errorsignals.
 3. The improvement of claim 1 wherein said binary signalgenerating means comprises: transducer means for producing an analogsignal proportional to the thickness of transported sheets of material;filter means coupled to said transducer means for removing rapidamplitude variations exhibited by said analog signal; and analog todigital converting means coupled to said filter means for generating amultibit binary signal proportional to said analog signal.
 4. Theimprovement of claim 1 wherein said selectively activatable gating meanscomprises a plurality of AND gates corresponding in number to the numberof bits included in each multibit binary signal; said AND gatesincluding first input terminals for receiving associated ones of saidbits included in a multibit binary signal and second input terminalsconnected in common relationship for receiving a gating signal suppliedthereto at selected intervals of time.
 5. The improvement of claim 1wherein said activatable detecting means comprises an AND gate having afirst input terminal for receiving said error signal and a second inputterminal for receiving an activating signal supplied thereto at selectedintervals of time.
 6. In combination with a sheet feeding mechanism,improved superposed sheet detecting apparatus for detecting thesuperposition of sheets of material fed by said sheet feeding mechanism,comprising: transducer means disposed at a predetermined location insaid sheet feeding mechanism for producing signals proportional to thethickness of sheets of material fed past said predetermined location;binary signal generating means coupled to said transducer means forgenerating multibit binary signals representative of said producedsignals; storage means for storing the multibit binary signalrepresentative of an initially produced signal; selectively activatablegating means interconnected between said binary signal generating meansand said storage means for selectively gating a multibit binary signalgenerated by said binary signal generating means into said storagemeans; comparison means having a first plurality of input terminalscoupled to said storage means and a second plurality of input terminalscoupled to said binary signal generating means for comparing thecontents of said storage means with each multibit binary signalgenerated by said binary signal generating means and for producing anerror signal when a generated multibit binary signal exceeds saidcontents of said storage means; activatable detecting means coupled tosaid comparison means and responsive to an activating signal suppliedthereto to detect said error signal; deflecting means coupled to saidactivatable detecting meanS and adapted to be interposed in the path ofsaid sheets of material fed by said sheet feeding mechanism in responseto a detected error signal for deflecting the sheets of material awayfrom said sheet feeding mechanism; and means for discarding the contentsof said storage means.
 7. The combination of claim 6 wherein saidstorage means comprises: settable counting means having a plurality ofinput terminals coupled to said selectively activatable gating means,said settable counting means being set to a binary count correspondingto said multibit binary signal representative of the thickness of aninitially transported sheet of material; and increment means coupled tosaid settable counting means for incrementing the set binary countthereof such that predetermined variations in the thickness ofsubsequently transported sheets of material do not produce errorsignals.
 8. The combination of claim 7 wherein said binary signalgenerating means comprises: filter means coupled to said transducermeans for removing rapid amplitude variations exhibited by each of saidsignals produced by said transducer means; and sample means coupled tosaid filter means for sampling at first selected intervals of time thesignal produced by said filter means and for generating a parallelmultibit binary signal proportional to said amplitude.
 9. Thecombination of claim 8 wherein said selectively activatable gating meanscomprises a plurality of AND gates corresponding in number to the numberof bits included in each multibit binary signal; said AND gatesincluding first input terminals for receiving associated ones of saidbits included in said parallel multibit binary signal and second inputterminals connected in common relationship for receiving a gating signalsupplied thereto at second selected intervals of time.
 10. Thecombination of claim 9 wherein said activatable detecting meanscomprises an AND gate having a first input terminal for receiving saiderror signal and a second input terminal for receiving an activatingsignal supplied thereto at third selected intervals of time; said ANDgate being deactivated when an initial sheet of material is fed pastsaid predetermined location.
 11. The combination of claim 10 whereinsaid means for discarding comprises reset means for receiving a resetpulse when a predetermined number of sheets have been fed past saidpredetermined location, said reset pulse being effective to clear saidmultibit binary signal from said storage means.
 12. The combination ofclaim 10 wherein said means for discarding comprises reset means forreceiving a reset pulse when said error signal is detected, said resetpulse being effective to clear said multibit binary signal from saidstorage means.
 13. In combination with a sheet feeding mechanism,improved superposed sheet detecting apparatus for detecting thesuperposition of sheets of material fed by said sheet feeding mechanism,comprising: transducer means disposed at a predetermined location insaid sheet feeding mechanism for producing signals proportional to thethickness of sheets of material fed past said predetermined location;binary signal generating means coupled to said transducer means forgenerating multibit binary signals representative of said producedsignals; storage means for storing the multibit binary signalrepresentative of an initially produced signal; selectively activatablegating means interconnected between said binary signal generating meansand said storage means for selectively gating a multibit binary signalgenerated by said binary signal generating means into said storagemeans; comparison means having a first plurality of input terminalscoupled to said storage means and a second plurality of input terminalscoupled to said binary signal generating means for comparing thecontents of said storage means with each multibit binary signalgenerated by said binary signal generating means and for producing anerror signal when a generated multibit binary signal exceeds saidcontents of said storage means; activatable detecting means coupled tosaid comparison means and responsive to an activating signal suppliedthereto to detect said error signal; and means coupled to saidactivatable detecting means and responsive to said detected error signalfor preventing the further feeding of said sheets of material by saidsheet feeding mechanism.
 14. The combination of claim 13 furtherincluding reset means for receiving a reset pulse when said error signalis detected, said reset pulse being effective to clear said multibitbinary signal from said storage means.
 15. The combination of claim 13wherein said storage means comprises: settable counting means having aplurality of input terminals coupled to said selectively activatablegating means, said settable counting means being set to a binary countcorresponding to said multibit binary signal representative of thethickness of an initially transported sheet of material; and incrementmeans coupled to said settable counting means for incrementing the setbinary count thereof such that predetermined variations in the thicknessof subsequently transported sheets of material do not produce errorsignals.
 16. The combination of claim 13 wherein said binary signalgenerating means comprises: filter means coupled to said transducermeans for removing rapid amplitude variations exhibited by each of saidsignals produced by said transducer means; and sample means coupled tosaid filter means for sampling at first selected intervals of time thesignal produced by said filter means and for generating a parallelmultibit binary signal proportional to said amplitude.
 17. Thecombination of claim 13 further including means for discarding thecontents of said storage means when a predetermined number of sheetshave been fed past said predetermined location.